Cocaine is a widely used drug of abuse. Recent surveys indicate there are approximately 1.5 million chronic cocaine users in the US. Effective treatments may devised to the degree that orderly and general knowledge of cocaine's effects are obtained. For example, repeated cocaine exposure can lead to an increased sensitivity to its excitatory effects, as measured by changes in locomotor activity. This increased sensitivity has been demonstrated in many experiments using rats and mice. The data obtained has been used to generate theories of human cocaine addiction, as increased sensitivity may relate to incentive to obtain the drug. However, these theories may only relate to data obtained with rats and mice, as the generality of these effects have not been demonstrated. Pigeons are also common animals used in behavioral preparations and provide a useful comparison species in which to conduct an extensive replication of previous research. Experiment 1 is designed to obtain basic descriptive data about cocaine's effects on locomotion in pigeons across a range of doses in order to assess the generality of previous findings. Experiment 2 will systematically replicate Experiment 1, in addition to investigating how prior history with cocaine influences subsequent exposure.